Published on 1 April 2019
Héloïse Chochois, « Infiltrée chez les physiciens », coll. « La physique autrement », Author provided

A physicist and professor at Université Paris-Sud, Julien Bobroff, head of the "Physics reimagined" team at the laboratory of solid-state physics (LPS - CNRS/Université Paris-Sud), invites you to refute 7 preconceived ideas on quantum physics that endure with the general public.

I have been popularizing my field of research, quantum physics, for many years. The general public is fascinated by quantum physics. It is also intimidated by it. Science popularizers sometimes use it to attract attention. The covers of magazines and books often rely on its mysterious aspect: "The ultimate secret of quantum physics finally revealed", "Life would be quantum!", "We all think quantum"... This is not without consequences. Many misconceptions are thus spread in this area of physics. Here are seven of the misconceptions that I hear most frequently, seven myths that do not stand the test of facts.

Do not worry, you do not need to know anything about quantum physics to read what is coming next, since I will tell you what quantum physics... are not!

1. "Quantum physics are uncertain"

This is false! Quantum physics are currently probably the most exact scientific discipline that humanity has ever conceived. They are able to predict certain properties with an accuracy of 10 decimal places, which are then verified accurately by experimentation! This is the case, for instance, for measurements of fine structure constants or quantum Hall effects. By comparison, this would be like being able, in a long jump event, to predict where an athlete will land to the nearest billionth of a meter by just observing his or her run and momentum!

 The uncertainty principle. Margaux Khalil, Janet Rafner, coll. _La physique autrement_, Author provided

One of the reasons for this misconception is Heisenberg's "uncertainty principle", a notion which is often misunderstood as suggesting that quantum physics are not accurate. This principle, which Heisenberg himself preferred to call "the principle of indeterminacy", shows that there is a limit to the accuracy of the measurement of two quantities at the same time, for example the velocity and position of a particle. Without going into detail, this indeterminacy comes from the same reason that makes it difficult to say precisely where a wave is in the sea, since it is necessarily a little spread out. But if we use quantum physics to calculate other quantities, such as the energy of atoms, or their magnetism, then they are incredibly precise. It is just a question of choosing carefully what you want to predict.


2. "It is not possible to represent quantum physics"

Quantum folding, Cyril Conton, coll. _La physique autrement, Author providedQuantum physics describe objects that are often "strange" and difficult to illustrate: wave functions, state superposition, presence probabilities, complex numbers... Often, we hear that they can only be understood with mathematical equations and symbols. However, as soon as quantum physics are taught or popularized, we, as physicists, constantly use illustrations – curves, metaphors, projections... It is quite simple: I do not know a quantum course devoid of images. Some books

are even entirely devoted to illustrating quantum physics through images. And it is just as well because images are key for students and even for experienced physicist to make mental representations of the objects they are manipulating. If we ask researchers working in the field, they themselves recognize that they "imagine" quantum matter.

The point that is debated is the accuracy of these images: it is indeed difficult to rigorously represent a quantum object. But is that not the case in many fields of science? The image of atoms obtained by a tunnelling microscope is only a representation of the tunnel current involving many arbitrary choices, colours, shadows, etc.

In our research team – "Physics reimagined" – we work on the very question of representation. We collaborate with designers, illustrators, and videographers, to "draw" quantum in all its shapes and forms: paper-folding, comic strisps, sculptures, 3D animations... For instance, we have designed a series of small animations that now populate Wikipedia articles, conferences and courses, although they are not completely accurate. But they do give the general public an idea of some key effects: duality, superposition, quantification... and are thus quantum images.

3. "Scientists themselves do not fully understand quantum science."


Richard Feynman,

one of the greatest names in the field, said himself: "I think I can safely say that no one understands quantum mechanics". But he then added: "I will tell you how nature behaves. It is all in the ‘how’". Feynman understood very well "how" quantum physics work, he even received a Nobel Prize for it, but not "why". And for quantum physics, this "how" is particularly surprising for any physicist familiar with traditional mechanics. Niels Bohr, one of the founding fathers of the field, sums it up well: "Anyone who is not dazed by quantum theory does not understand it.”

Physicists therefore understand what they are doing when they manipulate quantum formalism. They just have to "adapt" their intuitions to this new field and its paradoxes. This is not specific to quantum physics. Electromagnetism in the 19th century must have upset many scientists, when they had to admit that they were bathed in invisible waves, made of electricity and magnetism, which spread like light. The same goes for the space-time curves of general relativity.

4. "Quantum physics were created from scratch by a few brilliant theorists."

The whole history of physics contradicts this theory: at the very beginning, there was not just one brilliant theory born from a physicist's brain, but rather experiments conducted in the laboratory with unexpected results. Then, and only then, did theorists look at these results, try to understand them, implement new concepts, and use new tools...

Quantum physics are no exception to the rule: at the very beginning, scientists were puzzled by a few experiments such as the photoelectric effect, black-body radiation, and the light spectrum of atoms. Then came brilliant theorists such as Albert Einstein, Max Planck, and Niels Bohr, who understood that these experiments actually revealed the quantum nature of light and atom. After that followed some fundamental experiments, electrons bouncing strangely off nickel, silver atoms oddly deflected by a magnetic field, a metal that led perfectly to low temperature... And then again theories and concepts, duality, spin, superconductivity.

The invention of superconductivity. Credits: Little quantum stories, Marine Joumard, coll., _La physique autrement, Author providedPhysics are developed in these fertile round trips between experimenters and theorists, and experiments often come first, with a few exceptions (e. g. prediction of antimatter or the Higgs boson). In a small book I have just written, "My great quantum mechanic", I describe 11 of these key experiments in the history of quantum mechanics, and how they gave rise to major theoretical advances such as superconductivity, discovered in 1911 but only understood in 1957!

5. "Einstein was the worst enemy of quantum science."

Poor Einstein! He is often referred to as the fierce opponent of quantum physics. His famous sentence "Gott würfelt nicht" ("God does not play dice") has a lot to do with it. However, not only was Einstein not opposed to quantum physics, but better still, he was at its origin! In 1905, following the work of Max Planck, he wrote a founding article. He suggested that light was composed of small individual and quantified bodies – photons. He was even to receive the Nobel Prize for this work and not for his theory of relativity. That is not all. Einstein wrote several other key articles in quantum physics, such as the prediction of Bose-Einstein condensation, or the idea of stimulated emission that would lead to the invention of lasers.

Then why does he hold such a reputation? Everything comes from the debates he had with Niels Bohr, particularly on the notion of interpretation and quantum reality. Do quantum physics really describe the real world, which would then be intrinsically probabilistic? Are there no hidden variables that would allow us to better understand some of the greatest paradoxes of quantum physics? These fascinating debates culminated in an article he wrote in 1935 with Podolsky and Rosen in which he refuted the idea of non-locality. Later, experiments of entanglement and violation of Bell's equality would prove him wrong and show the absence of hidden variables: God finally seemed to be playing dice well... Let's just keep in mind that Einstein fully recognized the relevance of quantum physics to describe the world on a small scale, that he admired the accuracy of his predictions, but that he just had concerns with some of their implications, especially in relation to the notion of locality.

6. "Quantum physics are useless"

Like any fundamental research, quantum physics do not have to be "justified" as being useful. Understanding how the world works at the atomic level has, in my opinion, been one of the greatest achievements of the human mind, even if it was ultimately useless! But be reassured that quantum physics are probably the most useful discipline in modern physics. Because once physicists understood the way light, atoms and electrons worked, they were able to manipulate them. They had thus moved from the stage of comprehension to that of invention. The laser is often cited as a magnificent example of quantum invention. But it is not the only one: MRI in hospitals, light-emitting diodes (LEDs), flash memories, and hard disks were all invented by quantum physicists.

Lasers, levitation trains, or MRI, applications of quantum physics. My great quantum mechanic, Marine Joumard, Ed. Flammarion, Author provided

Even better, the transistor, this little component that is hidden in all microprocessors at the heart of your favourite smartphones and computers, the transistor which is at the origin of digital revolution, was invented by three physicists of quantum physics – William Shockley, John Bardeen, and Walter Brattain. And many researchers and engineers are working to create, in the lab, the quantum inventions of the future, such as quantum computers, but also new photovoltaic cells, thermoelectric components, new sources of light or new methods for telecommunications.

7. "Quantum physics could explain alternative medicines or other mysterious phenomena."

Many beliefs in paranormal phenomena or in certain "medicines" claim to be or are inspired by quantum physics. One of the most famous defenders of this approach, the Indo-American Deepak Chopra,

has developed a kind of quantum mysticism, where he uses a whole scientific jargon to justify some sort of New Age spirituality through "energy fields", "probability waves", "energy reharmonization", or "duality". All this leads him to suppose certain quantum links between thought, consciousness, matter and universe.

Similarly, "quantum medicines" offer treatment by considering the body as a "vibratory and energetic field", the seat of "vibratory states" or "bio-resonances". These "medicines" sell a whole range of equipment with learned names to "correct energy imbalances" or even measure "biofeedbacks".

Two dishonest methods are at work here. First, "to make scientific", i.e. to legitimize one's speech with scientific terms. This pseudoscience exploits the fact that quantum physics seem mysterious in order to explain other "mysteries". But, as we have just shown, quantum physics are not mysterious. They are verified by experiment not only in the laboratory but also in our daily lives, at work when we turn on an electrical outlet or use our smartphone. All the while, none of the phenomena described by these medicines or beliefs have a scientific basis nor have they been scientifically verified. And, above all, words have a very precise meaning in quantum physics that have nothing to do with their abusive use in these pseudosciences.

Another fraud consists in extrapolating the quantum properties to our scale. After all, our body is made up of atoms, which are quantum, so why not? Let us be clear: quantum properties such as state superposition or quantification cease at our scale. In recent years, we have been able to demonstrate this in the laboratory, thanks to experiments conducted by Serge Haroche, among others, who was awarded the Nobel Prize in 2012. Physicists have shown that as soon as an object interacts too much with its environment and is too big, it ceases to be quantum. On our scale, "objects" such as the human brain are simply too large, our earth temperatures too high, not to mention the air around us, to exhibit quantum behaviour.

A questionable equation. Solid-state physicists, Chloé Passavant, coll., _La physique autrement_, Author provided

However, I do not want to be a kind of moralizing censor who would decide the truth of the false from the top of his science. I do not condemn or judge those who want to test these practices. They fall within the scope of belief, not science, and each and everyone is free to indulge in them. I am just asking you to stop pretending that they are based on scientific foundations from quantum physics, because that simply is not true.

There you go. I hope that, with this short list, I have contributed to demystifying quantum physics, a scientific field which is, after all... like any other!

The original version of this article was published in French on The Conversation.